Genetical Analysis Of Interspecific Hybrids Between Cultivated Brassica Allotetraploids And Brassica Fruticulosa

Brassica fruticulosa Cirillo (twiggy turnip) can be a potential genetic source for crop improvement because it possesses resistance to white rust(Albugo candida), alternaria blight(Alternaria brassicae), cabbage aphid(Brevicoryne brassicae) and cabbage root fly (Delia radicum). In present study, interspecific reciprocal crosses between three cultivated Brassica allotetraploids and one wild species B. fruticulosa (FF,2n=16) were made and the trigenomic hybrids, allohexaploids and backcrossing progenies were produced. Chromosome pairing of trigenomic hybrids, allohexaploids and their backingcrossing progenies was investigated via dual genomic in situ hybridizaion (dual-GISH) to gain an insight into the genome affinity of Brassica. The main results were described as fellows:1. Reciprocal trigenomic hybrids (F.BC/BC.F,2n=25) were obtained between B. carinata (BBCC,2n=34) and B.fruticulos, however, hybrids (F.AB,2n=26; F.AC,2n=27) were produced only with B. fruticulos as female crossing with B. juncea (AABB,2n=36) and B. napus (AACC,2n=38). These hybrids showed an intermediate morphology and were sterile for male and female except those from B. carinata. The allohexaploids (FF.AABB,2n=52; FF.AACC,2n=54; BBCC.FF,2n=50) showed growth vigor and had the larger stature than the trigenomic hybrids, but were still male sterile except the one (FF.AABB). They produced backcross progenies with expected chromosome complements (F.AABB,2n=44; F.AACC,2n=46; BBCC.F,2n=42).2. All the triploids showed high frequency of bivalents during diakinesis and metaphase I (MI) of meiosis. The average chromosome association was0.3â…¢+4.3â…¡+17.5â…  in F.AC and0.1â…¢+4.9â…¡+15.9I in F.AB. The two F.BC/BC.F hybrids showed quite similar pairings configuration, and the average chromosome association was0.1III+4.0â…¡+16.7I in F.BC and0.1â…¢+3.9â…¡+16.9I in BC.F. In allohexaploids, chromosomes were mainly paired as bivalents at diakinesis and segregated equally at anaphase I (AI) during meiosis of pollen mother cells (PMCs). But univalents and multivalents were aslo observed with low frequency. 3. By dual-GISH, autosyndetic bivalents and allosyndetic bivalents were detected PMCs of the trigenomic hybrids.At the same time, a closer relationship of F and B genomes than F and A/C genomes was revealed. The chromosomes in PMCs of allohexaploids were predominantly paired as bivalents. Although the bivalents were formed mostly within the same genome, allosyndetic quadri-/hexavalents involved any two genomes were observed. Autosyndetic quadrivalents within the same genome of A, B and C were also observed but not theF genome.4. Phenotype of progenies from allohexaploids through backcrossing was similar to their respective allohexaploids. Chromosomes of crop Brassica predominantly paired as bivalents with their homology chromosomes. Chromosomes of B. fruticulosa usually appeared as univalents. Whereas, bivalents and trivalents formed between F and A/B/C genomes were also observed at low frequence.2-5F genome chromosomes were observed in mitotic cells of BC2progenies.5. SRAP molecular marker analysis indicated that genetic changes were common in all hybrids. The percentage of deleted bands of B. fruticulosa was higher than that of Brassica allotetraploids in hybrids. The percentage of new bands was low but found in every hybrid.